I’m assuming you put a waste board over the wasteboard to make it last a bit longer? thinking something simple like 1/16 or less poster board or something to make sure I can set the cut depth to make sure the bit makes it through all the way (especially wood that’s not planed) and prolonging the silkscreen a bit
I always considered the factory wasteboard to be part of the structure and keep a piece of sacrificial MDF on top of that. The top MDF gets surfaced and destroyed eventually and I throw it out when it is bad enough and replace. My original wasteboard still looks new…but I never actually see it since it is always covered.
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The silk screen is nice but no requirement, so for depth critical work a skimmed surface is a must.
Once that is done you can zero of the waste board, elevate the bit say 13mm and jog it to X/Y zero.
With cut depth set to 13mm you will cut exactly to the right depth.
I use double sided tape to affix the material before carving and if I want I can get the bit to cut one of the two tape layers and not the other 
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I use a piece of tempered hard board over the waste board until it is too carved up to be any good. My waste board only has a few slight skim marks on it, a one 1/8" diameter hole and several laser burns on it.
The benefit to me of the silkscreen, and maybe it’s not a big deal in the long run but I had a case where using the 4x8 commercial CNC at the local maker place, I had a 8 foot piece of lacewood i was cutting. I measured to the edge from the board to ensure the workpiece was parallel to Y axis (cutting 30 patterns along the length). I did not measure that the board itself was square and in fact gradually got wider as it went. not by much but about half way through I noticed my cut outs were drifting (compounding I guess is that I had anchored the design to the opposite side)
So a quick visual that a piece of material is itself “square” and then easy squaring with the X and Y axis is why i preferred the silkscreen vs blank / DIY. So, at minimum a sanity check that the piece is lined up. Obviously if i semi-permanently cover the silkscreen all up then defeats the point.
To date (with the commercial machine) I haven’t done anything that was so “depth critical” that any small variances in the table (low density fiberboard / vacuum) would make a difference assuming z-probe of the material anyway.
Thanks for mentioning it… something to look out for / waiting on my x-carve.
Yeah dunno… after it was done cutting I measured the whole thing wondering how I didn’t get it lined up and the board was 1/4" wider at one end. Maybe just this specialty lacewood is more likely than not to not quite conform to dimensions?
My wife has all kinds of plans for wood from the same place in town so was figuring a quick eyeball with the grid might be a nice benefit for however long it lasts before I have to skim… so was looking for ideas of the thinnest scrap piece to back individual work pieces with that people were using. looking at other threads sounds like 1/8 MDF